Republican Leaders Map a Strategy to Derail Donald Trump

Republican leaders adamantly opposed to Donald J. Trump’s candidacy are preparing a 100-day campaign to deny him the presidential nomination, starting with an aggressive battle in Wisconsin’s April 5 primary and extending into the summer, with a delegate-by-delegate lobbying effort that would cast Mr. Trump as a calamitous choice for the general election.

Recognizing that Mr. Trump has seized a formidable advantage in the race, they say that an effort to block him would rely on an array of desperation measures, the political equivalent of guerrilla fighting.